Selective functional properties of dual atrioventricular nodal inputs - Role in nodal conduction, refractoriness, summation, and rate-dependent function in rabbit heart

Background The atrioventricular node receives its activation signal from the low crista terminalis and low interatrial septum, the summation of which is believed to favor conduction. A functional asymmetry between the inputs is also believed to be involved in nodal reentrant rhythms. We studied the selective functional characteristics of nodal inputs and determined their role in nodal conduction, refractoriness, summation, and rate-dependent function. Methods and Results The nodal properties of recovery, facilitation, and fatigue were characterized with stimulation protocols applied with varying phases between the two inputs in isolated rabbit heart preparations. The effects of the input phase, nodal functional state, and input reference on the nodal conduction time, recovery time, and refractory periods were assessed with multifactorial ANOVAs. It was found that the phase of stimulation significantly affected nodal conduction time but not the refractory periods or the time constant of the recovery. Each input could show longer and shorter conduction time than the other depending on the stimulation phase, input reference, and coupling interval. These effects were similar for different nodal functional states. However, pacing and recording from the low crista resulted in similar conduction and refractory values than did pacing and recording from the low septum. Input summation did not increase the otherwise equal efficacy of individual input in activating the node. Nodal surface recordings confirmed this functional symmetry and equivalent efficacy of the inputs and showed that input effects were confined to the proximal node. Conclusions The two nodal inputs have equivalent functional properties and are equally effective in activating the rate-dependent portion of the node. Input interaction affects perinodal activation but not the rate-dependent nodal function.